(1) Field of the Invention
This invention relates to a process and apparatus for producing false-twisted polyester yarns having enhanced tenacity, elongation and crimp stretchability and having such a good dyeability that dyeing can be accomplished under normal pressure with a disperse dye, by heat-treating a polyester yarn and continuously subjecting the yarn to false twisting.
(2) Description of the Prior Art
As a typical instance of the conventional process for false-twisting or draw-false-twisting polyester yarns, especially polyethylene terephthalate yarns, there can be mentioned a process disclosed in Japanese Unexamined Patent Application No. 48-35,112/73. A false-twisted yarn obtained according to this conventional process is excellent in various properties such as crimpability, tenacity, dimensional stability, heat resistance and wash-and-wear property and is utilized in various fields. However, polyethylene terephthalate fibers and false-twisted yarns thereof are poor in the dyeability and must be dyed at a high temperature such as about 130.degree. C. Accordingly, it is necessary to employ a special apparauts for the dyeing operation, and furthermore, it is considerably limited that polyethylene terephthalate fibers are blended with fibers in which the physical properties are deteriorated by high-temperature high-pressure dyeing, such as wool, acrylic and Spandex fibers.
Attempts have been make to improve the dyeability of polyethylene terephthalate fibers and false-twisted yarns thereof for enabling these fibers and yarns to be dyed under normal pressure. For example, there is known a process using a dyeing accelerating agent called "carrier". This process, however, has several problems. For example, since the carrier is irritating and harmful to human bodies, the working environment of dyeworks is contaminated. It is difficult to dispose the waste dyeing solution. Furthermore, it often happens that dyeing specks called "carrier spots" are formed by insufficient emulsification of the carrier and the carrier remains in a dyed article to degrade the color fastness to light of the dyed article. Moreover, the carrier dyeing causes changes in the mechanical properties of polyethylene terephthalate fibers and false-twisted yarns thereof, for example, reduction of the tenacity and increase of the elongation.
It is known that the dyeability of polyethylene terephthalate can be improved by copolymerization with a metal sulfonate compound or a polyether. Although the dyeability is improved in this modified polyester, the modified polyester has problems in that polymerization or spinning is difficult, the mechanical and thermal properties possessed inherently by polyethylene terephthalate are degraded and the color fastness is reduced. Consequently, since a third component acting as a dye receptacle for dyeing the polymer is introduced for modifying the chemical properties of the polymer, reduction of heat resistance and mechanical properties possessed inherently by polyethylene terephthalate cannot be avoided by the improvement of the dyeability.